Induction heating apparatus



Oct. 16, 1945. v. w: SHERMAN INDUCTION HEATING APPARATUS Filed Feb. 25, 1943 FIG.2.

A M y 7 mm m E W I m r M T 5 g w A /WW R w .v. n /V:

FIG. 3,

flux of the respective coil turns thereby to set spending parts in the several views.

Patented Oct. 16, 1945 INDUCTION HEATING APPARATUS Vernon W. Sherman,

Federal Telephone Summit, N. J., assignor to & Radio Corporation, New

York, N Y., a corporation of Delaware Application February 25, 1943, Serial No: 477,086

i 6 Claims. This invention relates to the art of high frequency induction hardening of metal work pieces and more particularly to the surface hardening of bearing shafts and the like. The object thereof is to provide an improved apparatus and meth- 0d operating to effect a more uniform distribution of the heating and resulting hardening action throughout the length or surface area of the portion of the work being treated.

It has been found, for instance, that in the surface hardening of a cylindrical bearing shaft by means of a high frequency coil enclosing the hearing portion under treatment in spaced, coaxial relation thereto, that in some instances and as a result of the counter magnetomotive forces set up within the body of the work piece and the resultant effect upon the flux flow that there occurs an unevenness in the depth of the hardening. This variation of the heated depth considered longitudinally of the work piece is in the nature of a surface ripple of undulating or wave conformation wherein the crest of the hardened wave area or greater depth of hardening occurs atp'oints under each turn of the heating coil. To overcome this objectionable variation of hardening depth there is provided a. shield element positioned concentric with the heating coil and in suitable spaced relation thereto as to be in coupled relation within the path of the magnetic up local area counter magnetomotive forces influencing or controlling the resultant flux field so as to compensate for the aforesaid wave effect and accordingly to produce a more uniform depth of heating of the surface under treatment.

The features of and advantageous effects of the present invention will be more clearly understood by reference to the drawing herewith wherein like reference characters are applied to the corre- In the drawing:

. Fig. l is a diagrammatic view of an induction heating coil arrangement as heretofore employed and showing the non-uniform or ripplingv of the heated depth which commonly occurs;

Fig. 2 is a corresponding view illustrating the employment therewith of the shield element of the present invention to have a restraining or compensating control of the primary coil flux to obtain uniform heating depth;

Fig. 3 is a perspective v ew of the improved heating apparatus comprising the coil and surrounding split sleeve member.

In the process of inductively heating the work piece, counter magnetomotive forces set up by 55 the flow of current in the surface of the work piece will have magnitude depending upon various factors such as coemcient of coupling, wall thickness, temperature, magnetic permeability, resistivity and nature of material of the work piece. Such counter magnetomotive forces tend to distort the primary magnetomotive forces of the individual turns of the heating coil in the arrangements as customarily employed resulting in non-uniform depth of heating of the work piece surface layers.

An. illustration thereof is diagrammatically shown in Fig. 1 wherein is shown the employment of a single heating coil A in the customary manner for induction heating of the work piece W centrally enclosed within the coil in suitable spaced relation thereto, the coil being energized by the usual high frequency source conventionally indicated. In the heating by this customary induction heating arrangement there results an unbalanced effect upon the field of the primary coil by reason of the various counter magnetomotive forces set up within the body of the work p ece giving a fiuxflow resultant and a cumulative effect of heating which is uneven in depth, the variation thereof considered longitudinally of the work piece being in the nature of a surface area ripple or undulating wave conformation wherein the crest or major heating depth occurs in a transverse plane of each heating coil turn as diagrammatically indicated in Fig. l and wherein the minor depth of heating occurs in the horizontal plane intermediate of the coil turns as indicated.

In accordance with the present invention, and for the purpose of overcoming the objectionable variation in depth of the heating and resulting hardening action there is provided, as shown in Fig. 2, a shield member S of high electric conductivity material which is in the form of a longitudinally split sleeve having a vertical opening 4 extending the length thereof. In this arrangement a helicalheating coil A of uniform diameter is employed surrounding the work piece W which as illustrated is in the form of a cylindrical shaft and is positioned within the coil to be coaxial therewith in suitable spaced relation to the coil for the desired inductive heating; the coil shown being in series with a high frequency circuit C. The equalizer shield member S, as illustrated, is correspondingly coaxial with the heating coil and positioned to surround the coil in spaced relation thereto and is of a length or overall vertical dimension extending slightly above and below the induction heating coil A.

The equalizing shield in the arrement disclosed will minimize distortion of the primary magnetomotive forces, incident to the countermagnetomotive forces set up within the work,

and thus insures more uniform current flow in distorting effect upon the magnitude of the countermagnetomotive forces induced by the various areas of the work piece so as to compene sate for or nullify the tendencies toward distortion. of the efiective iiux field with the result of .auniform depth of heating as indicated. Ac-

cordinglythe differences of flux density induced in neighboring areas of the shield cause eddy currents to now in the shield in such fashionas to set up countermagnetomotive forces to restore the flux of each area to a common level. 'Ijhe normal distortion, such as indicated in connection with Fig. 1 is in consequence resisted and flux is constrained to thread the work piece in a substantially uniform manner.

As shown in Figs. 2 and 3, the shield 'Sls grounded by a lead 7, thereby providing a static discharge from the shield element offering protection to andagainst interference by the prom imity thereto of external bodies and thereby contributing to the desired uniformity of the heating results. Also a connection from the coil to the shield-may be provided as indicated thereby to include the shield in series circuit relation with the lead 3'.

Thus by grounding of the central turnof the coil the capacitive voltage of each end turnto external ground such as frame and work piece, is"

minimized. The static shield, thus afforded, also equalizes, voltages between the turns of the coil by functioning as a capacitive voltage divider across the series of turns comprising the coil. This minimizes the tendency toward abnormal voltage concentration in any one part of the coil and in consequence reduces the danger of breakdown.

The source of high frequency current employed may desirably have a frequency of 1,000,000 cycles per second or more, being preien' ably of the order of 5,000,000 cycles per second or above, thereby shortening the interval-of heatin with reduced ration of heat conduction losses permitting of self quenching action by the nonheated body metal of thework piece.

It will be obvious from the, disclosure that I varied modifications may be made therein without departing from the scope of the invention as defined in the appended claims. 7

What is claimed is: 1. An induction heating apparatus for the surface heating of work pieces by induction, comprising an inductor of a plurality of turns adapted to be positioned in inductive heating rela-..

tion to the work and an equalizing shield member of high electric conductivity materialpositioned in magnetically coupled relation to the heating inductor at the opposite side thereof from the heating field and work to have opposing and neutralizing influence upon the heating flux field to aceaeie magnetcmotive forces set up within the work,

said shield being longitudinally separated to be of a non=closed coil formation and of a size to be longitudinally coextensive with the inductor and of a form substantially to surround the inductor and means for energizing the heating inductor with a high frequency current.

2. An induction heating apparatus for the surface heating of the work pieces by induction,

comprising a heating coil of a plmality of turns adapted to be positioned in inductive heating re lation to the work and an equalizing shield mem= ber ofv high electric conductivity material positioned in magnetic coupled relation to the heat= ing coil at the opposite side thereof fromthat of the work to have opposing and corrective influence upon the heating iiux held to counteract ,a spiral coil of a plurality of turns adapted to be positioned in inductive heating relation to the work and an equalizing shield member of high electrical conductivity materlm and or longitudinally split cylindrical sleeve formation extending longitudinally coextensive with the coil and positioned to substantially surround the heating coil.

in magneticallycoupled relation therewith at the opposite side thereof from the heating field and work to have opposing and neutralizing action I upon the heating flux field to counteract distortion thereof incident to countermaguetomctive forces set up within the work and means for energizing the heating coil with high frequency currents.

4. An induction heating apparatus of the charaoter described adapted for heating work pieces by induction comprising a spiral heating coil or a plurality of turns and of substantially uniform diameter and adapted to be positioned in inductive heating relation to the work and an equalizing shield member of high electrical conductivity material and of. longitudinally split cylinder formation or a size extending longitudinally coextensive with the coil andpositioned concent'rically of and substantially to surround the coil in magnetically coupled relation thereto so as to have opposing and compensating influence upon the. heatlngflux field to counteract distortion thereof incident to countermagnetomotive forces and means for energizing the. heating coil with high frequency current and an electrical connection between the coil and'shield.

5. an induction heating apparatus for the surface heating of work pieces by inductiomcomprising an inductor of a plurality of turns adapt-- ed to be positioned in inductive heating relation to the work, an equalizing shield member of high electric conductivity material positioned in ma netically coupled relationto the heating inductor at the opposite side thereof from that of the heating field and work to have opposing and neutralizing influence upon the heating flux field to counteract distortion thereof incident to countermagnetomotlve forces set up within the work, said shield being. longitudinally separated to be of anon-closed coil formation andof a length extending longitudinally at least, equal to the length of the coil and of a form substantially to surround the inductor, means for energizing the heating inductor with a high frequency current and a groundedconnection to the equalizing shield providing a static discharge therefrom.

6. An induction heating apparatus for the surface heating of work pieces by induction comprising a heating coil of a, plurality of turns adapted to bepositioned in inductive heating relation to the work, an equalizing shield member of high electric conductivity material positioned in magnetic coupled relation to the heating coll at the side thereof opposite to the-work to have opposing and corrective influence upon the heating flux field, said shield being longitudinally separated to be of a non-closed coil formation and having a length at least equal to that 01? the coil and arranged to surround the inductor with a terminal end portion of the inductor passed through the separation therein, means for energizing the heating coil with a high frequency current, a grounding-connection to the shield member providing a, static discharge therefrom and an electrical connection from the heating coil to the shield member substantially as described.

- VERNON W. SHERMAN. v 

